Solvent refining of fatty oils



Patented Sept. 26, 1950 soLvEN'r REFnvING or FATTY oTLs Herbert J. Passino, Englewood, N. J., assigner to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application January 13, 194s, serial No. 1,942

(ci. 26o-42am 8 Claims.

This invention relates to improvements in a method of separating mixtures of high molecular substances, such as animal fats and oils, vegetable oils and waxes and similar mixtures of non-hydrocarbon organic substances or mixtures of high molecular hydrocarbons with high molecular non-hydrocarbon substances into fractions having different compqsitions. More particularly, the invention relates to improvements in methods of fractionating such oils into extract and railinate phases with a solvent whose miscibility with the oil decreases with increasing temperature. Still more particularly, the invention relates to a method of rening the railinate phase byrecycling a portion of said phase to the fractionating zone, with or without the addition of solvent.

A principal application of the improved process is the treatment of fatty. oils to separate a @relatively small proportion of the oil as the desired product. An example of this type of operation is the treatment of natural oils to separate therefrom fractions which are concentrated in vitamins. A second application of the invention is in the treatment of oils whose constituents all have molecular weights of the same order of magnitude in order to separate the oil into fractions in accordance with differences in chemical constituents; it is desirable to accomplish this separation without chemical treatment. An example of this application of the invention is the treatment of palm oil to obtain a concentrate of the pro-vitamin A carotenoid,

as described in Patent No; 2,432,021, entitled.

Concentration of Vitamin A Carotenoids" and f assigned to The M. W. Kellogg Company. As

described in that'case a carotenoid concentrate may be obtained in the railinate phase of a continous counter-current fractionation of palm oil with a normally gaseous hydrocarbon solvent, preferably propane. The method disclosed herein provides a means for further refining the carotenoid concentrate.

In other cases, the invention provides a means for salvaging an extract material carried down into the raiiinate phase. For example, in the decolorization and reilningj of tallow by solvent fractionation with propane in a continuous counter-current tower system, the crude tallow may contain as little as one per cent of color bodies or other undesirable impurities. Conventional fractionation makes it possible to obtain a very highV grade, decolorized tallow from the extract by fractionating the crude tallow into a 97 per cent extract fraction and a raillnate fraction; this, however, represents a loss of three per cent tallow in the railnate. It is possible, of course, to subject the raffinate to a second propane fractionation but this is expensive and requires` an additional tower and a second counter-current stream of propane. According to the present method a raflnate fraction of three per cent or more is withdrawn but' the greater portion of it is reintroduced into the fractionating tower at a point above the lower phase level and above the point at which the solvent is introduced. 'I'he recycled ranate is thus all or partly dissolved and is subjected to rectication by being again precipitated in the lower portion of the tower. In one preferred form, a small amount of propane is added to the recycled portion of the raffinate in order to facilitate its flow and its conversion, at least in part, to upper phase solution. It is to be noted, however, that the quantity of propane which must be added at this point is much less than would be needed for a second fractionating tower so that it is a much more economical means of scavenging all possible extract matter from the raffinate.

Furthermore, the effects ofthe addition of propane to the recycled raffinate can be used to achieve the same results as ifa much larger quantity of propane were introduced directly into the fractionating tower. In many cases it is desirable but costly to have a very high ratio of solvent to oil treated. For example, if the tower is operated with a charge of 10 volumes of solvent for each volume of oil, and the addition of 5 volumes of solvent for each volume of ranate recycled, the results in the case of some oil will be substantially the same as if the solvent to oil charge ratio were much greater than 10; actually, the-total propane employed will be only slightly greater than4 10 times the volume of charge oil because the amount of raffinate recycled per hour is small relative to the charge oil so that the amount of propane necessary tol is obtained from the ralnate fraction of soybean oil by recycling a portion of the raffinate to the extract phase in order to achieve a cleaning action. The color bodies which are present in the soybean oil come down with a lecithin in the bottoms but these may be readily separated by a subsequent fractionation.

Although the invention is not limited to any particular type of apparatus it may be better understood from the description of a simple form of a solvent extraction tower shown diagrammatieally in the drawing. A vertical fractionation' tower I3 is shown with the usual propane inlet and valve Ila near the lower or raiiinate end I2 and an oil charging line I3, through` which the raw charge oil is introduced into tower I0, preferably at some point in the middle third of the tower. Pressure and temperature conditions controlled to cause all or a portion of charge oil introduced through line I3 to go into solution into the solvent introduced through line Il. 'I'his solution is then subjected to treatment, such as a gradient of upwardly increasing temperature within the tower provided by any convenient means such as heating coils I4 so as to cause an upper or extract phase l5 and a lower or raffinate phase I6 to be formed therein, separated at some point by an interface I1. Conduit withdrawal means I3 and I9 for continuously or intermittently withdrawing the extract and raflinate phases are provided at the upper and lower ends respectively. Preferably, the extract conduit I8 is introduced into a separating means at a substantially lower pressure in order to flash off part of the solvent through line 2| and to withdraw the extract in concentrated form through line 22. A portion of the extract is recycled to tower I0 through line 23 by means of pump 23a for refluxing purposes, the balance being passed through a pressure reducing valve 24 typical solvent such as propane is employed the tower I0 may operate under a pressure of nearly 600 lbs. per sq. inch, separator 20 and storage tank 30 at a pressure of about 200 lbs. per sq. inch, and separator at substantially atmospheric pressure; pump 3| serves as an economical means of obtaining an elevated pressure at tower I0.

The rafllnate withdrawn through discharge conduit I3 at the bottom of tower I0 is divided into portions which are determined by the setting of valves 32 and 33 into a recycled portion, usually more than 50 per cent, which is reintroduced into tower I0 by means of line 34 at any point that may be selected by the manipulation of valves 35, 36, or 3l, or into charge oil feed line through valves 33. It is necessary for the ei'lective application of my method that the recycled rainate be introduced into tower I0 at a point not lower than the interface level |'I, which is usually but not necessarily at a lower level than the point of entry of the propane line I I. A pump 39 may conveniently be employed for recycling the ralnate. Recycling may be facilitated by means of a small amount of propane introduced through line 40 by opening valve 40a. In the case of most oils, it will be found possible to greatly economize in the use of propane by very substantially reducing the propane introduced into extraction tower I0 through line I I by partially closing valve IIa while at the same time opening valve a only slightly. In many cases the enect is the same as if the solvent to oil ratio within tower I0 were greatly multiplied although the actual amount of propane employed remains the same. The reason is that only a small amount of propane is required to be passed through line 4l to thoroughly dilute the raillnate recycled through line 34. 0n the other hand. the invention is not limited to the recycling of raillnite with the introduction of propane through line 40a but includes the recycling of ralnate when not diluted and, indeed, even in cases in which it is desolventized. For example, fractionation conditions within the tower lll may be radically altered by recycling ralnate material which has been cooled or neutralized with alkali before reintroduction into tower I0.

The bottom product, or at least a portion of it, may be conveniently stripped of propane in an intermediate pressure evaporator 4I, the separated solvent being delivered through line 42 to intermediate pressure line 2|. The product oil is then withdrawn from intermediate pressure evaporator 4| through line 43 to a final separation at atmospheric pressure in an atmospheric pressure evaporator 4'I from which raillnate product is withdrawn through line 44 and solvent is withdrawn through line 45 to be recompressed by compressor 46 and returned to intermediate pressure line 42.

Although the invention is not limited to any particular solvent fractionation system and may be used in connection with solvents such as methanol, isopropyl alcohol, phenol, furfural. and the like, it is uniquely adapted for use in fractionation systems employing solvents of low critical temperature,in which the extract and ramnate phases are formed in a range between the temperature of greatest miscibility and the critical temperature, for instance, normally gaseous hydrocarbons, particularly propane, when employed in temperature ranges between critical temperature of F. below critical.

The invention is particularly applicable in the solvent fractionation of a high molecular weight mixture by means of a solvent Whose critical temperature is not higher than 450 F. wherein the solvent is introduced at a low point in a vertical solvent fractionation zone and the high molecular weight mixture is introduced at a point substantially above the solvent charging point, and wherein the solvent fractionation treatment is carried out at temperatures between the critical Y temperature of the mixture and 100 F. below the critical, and in which miscibility of the high molecular weight mixture and the solvent decreases with rising temperature.

Furthermore, the invention is adapted either to concentrating a pure product in the raffinate phase or to achieving a higher recovery in the extract phase.

The invention will be illustrated by reference to an example which relates to the fractionation of soybean oil to obtain phosphatides therefrom Iby means of solvent extraction with propane in accordance with the method disclosed herein.` A commercial soybean oil was subjected to treatment with propane solvent in a combination extraction and rectification tower having an inside diameter of three inches and a height of 60 feet. The oil was charged to the tower at the point about 36 feet from the top at a rate of approximately 4,000 cubic centimeters per hour. A pro'- pane solvent was charged to the tower about 58 feet froml the top at a rate of between 40,000 and 120,000 ccs. per hour, i. e. at a solvent to oil vollunetric ratio in the range from :1 to 30:1. The tower was maintained at between 400 and 500 pounds per square inch pressure. After equilibrium conditions were established in the tower, the oil charged was fractionated to an overhead extract of 98 per cent and a bottoms raffinate of 2 per cent; thus the bottom yield was about 80 ccs. per hour. In the absence of any recycling of the railinate to the tower, it was necessary to withdraw a bottoms of at least three per cent in order to separate all of the phosphatides therein. When, however, the raiinate was recycled (without the addition of any solvent) it was found possible to concentrate the phosphatides in the bottom two per cent. Thus, the bottoms Iobtained by operation without recycling is about 60 per cent phosphatides at the maximum; with recycling, the bottoms were about 85 per cent phosphatides, so that less tallow is lost and a better -bottoms product is recovered. The amount recycled was varied from 10 ccs. per hour to 200 ccs. per hour, i. e. recycled to yield ratios ranging from 1/2:10. sample of soybean oil used in thistest, an intermediate recycled to yield ratio of approximately 5:1 seemed best. It was/also found possible to operate at a much lower solvent to oil ratio and yet achieve superior results.

I claim:

1. In the solvent fractionation of a high molecular weight mixture containing a fatty oil by means of a solvent whose critical temperature is not higher than 450 F. wherein the solvent is introduced at a low point in a vertical solvent fractionation zone and the high molecular weight mixture is introduced at a point substantially above the solvent charging point, and wherein the solvent fractionation treatment is carried out at temperatures in the range between the critical temperature of the mixture and 100 F. below the critical, and in which miscibility of the high molecular weight mixture and the solvent decreases with rising temperature, the improvement comprising withdrawing rainate solution from'a point below the point of introduction of the high molecular weight mixture, and reintroducing a portion of said withdrawn rainate into said solvent fractionation zone at a point above the point of introduction of said solvent, and not higher than the point of introduction of said high molecular Weight mixture.

2. A method as described in claim 1 in which additional solvent is introduced into said recycled portion.

3. An improved method of concentrating lecithin which includes the steps of continuously introducing a lecithin-containing oil into a vertically extended fractionation zone at a point substantially removed from the lower end thereof; continuously introducing into said fractionation In the case of the particulark zone near the lower end 'thereof a solvent for said oil having a substantially lower density and boiling point than said oil, and a critical temperature not higher than 450 F.; contacting said oil and said solvent in a temperature range between the critical ,temperature of the mixture and F. below the critical under pressure suicient to maintain the mixture in a liquid condition; continuously withdrawing an extract phase substantially free of lecithin from the upper portion of said fractionation zone; continuously withdrawing a raffinate phase concentrate in lecithin from a point near the lower end of said fractionation zone; and recycling a substantial portion of said raffinate to said fractionation zone at a point substantially above the point of introduction of said solvent and not higher than the point of introduction of said oil.

4. A method as described in claim 1 in which said recycled portion comprises more than 50 per cent of the withdrawn rainate.

5. A method as described in claim 1 in which said recycled portion is subjected to cooling before being recycled.

6. A method as described in claim l in which said recycled portion is subjected to neutralization with alkali.

7. In the solvent treatment of a fatty oil to remove a relatively small fraction of said oil in a raffinate wherein a solvent having a density and boiling point substantially lower than said oil and a critical temperature not higher than 450 F. is contacted with said oil in a vertically extended fractionation zone in a temperature range between the critical temperature of the solvent-oil mixture and 100 F. below the critical, and in which miscibility of the oil and the solvent decreases with the rising temperature, the improvement comprising: withdrawing raffinate solution from a point below the point of introduction of said oil at a rate substantially in excess of the desired bottom fraction; and reintroducing said Yexcess into said fractionation zone at a point substantially above the point of introduction of said solvent, and not higher than the point of introduction of said high molecular weight mixture.

8. A method as described in claim 1 in which soybean oil is treated to concentrate phosphatides in a bottoms fraction of less than 10 per cent.

HERBERT J. FASSINO.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,118,454 Schaafsma May 24, 1938 2,139,392 Tijmstra Dec. 6, 1938 2,285,795 Batchelder June 9, 1942 2,432,021 Larner Dec. 2, 1947 

1. IN THE SOLVENT FRACTIONATION OF A HIGH MOLECULAR WEIGHT MIXTURE CONTAINING A FATTY OIL BY MEANS OF A SOLVENT WHOSE CRITICAL TEMPERATURE IS NOT HIGHER THAN 450* F. WHEREIN THE SOLVENT IS INTRODUCED AT A LOW POINT IN A VERTICAL SOLVENT FRACTIONATION ZONE AND THE HIGH MOLECULAR WEIGHT MIXTURE IS INTRODUCED AT A POINT SUBSTANTIALLY ABOVE THE SOLVENT CHARGING POINT, AND WHEREIN THE SOLVENT FRACTIONATION TREATMENT IS CARRIED OUT AT TEMPERATURES IN THE RANGE BETWEEN THE CRITICAL TEMPERATURE OF THE MIXTURE AND 100* F. BELOW THE CRITICAL, AND IN WHICH MISCIBILITY OF THE HIGH MOLECULAR WEIGHT MIXTURE AND THE SOLVENT DECREASES WITH RISING TEMPERATURE, THE IMPROVEMENT COMPRISING WITHDRAWING RAFFINATE SOLUTION ROM A POINT BELOW THE POINT OF INTRODUCTION OF THE HIGH MOLECULAR WEIGHT MIXTURE, AND REINTRODUCING A PORTION OF SAID WITHDRAWN RAFFINATE INTO SAID SOLVENT FRACTIONATION ZONE AT A POINT ABOVE THE POINT OF INTRODUCTION OF SAID SOLVENT, AND NOT HIGHER THAN THE POINT OF INTRODUCTION OF SAID HIGH MOLECULAR WEIGHT MIXTURE. 